1. Field of the Invention
The present invention relates in general to a braking system of a vehicle, and more particularly to improvements in or relating to a hydraulic circuit of an anti-locking breaking system for use in an on-land vehicle.
2. Description of the Prior Art
In general, it is known that with the use of an anti-lock braking system in a passenger carrying vehicle which operates at a relatively high speed, the rotating velocity of the vehicle wheels is detected by way of a revolution velocity sensor, and the thus-obtained speed data is electronically differentiated to provide a wheel acceleration signal at an electronic control section. In accordance with this wheel acceleration signal, there is determined a sign or transient symptom of a tendency of a wheel or wheels of the vehicle to become locked when the brakes are applied during cruising of the vehicle at a relatively high speed. Upon such determination a suitable operating command is given to a modulator or hydraulic regulating mechanism, so that a suitable counter-operation to ensure maneuverability or operating stability of the vehicle may be taken quickly, and braking force is applied in such a manner that the vehicle wheels are allowed to slip to an appropriate extent, so that the vehicle may positively be stopped within the shortest possible braking distance. In this connection, attention is directed to Japanese Patent Laid-Open Application No. 33,556/1983 (Tokukaisho No. 58-33556).
In such a typical construction of the anti-lock braking system as stated above, it is generally known that while there is employed control means to enable a hydraulic braking force to be relieved to the reservoir of a master cylinder in a hydraulic braking circuit, while the operating pressure of the hydraulic fluid is regulated at the modulator or hydraulic regulating mechanism, it is very possible that air is trapped or introduced into the hydraulic fluid circuit when the relieving of such braking pressure is made irregularly at the modulator. When such air is entrapped within the hydraulic circuit for relieving a braking pressure from the modulator to the reservoir of the master cylinder, this particular local zone of the hydraulic circuit is eventually detected by the modulator as being in a negative working pressure condition. This then would affect improperly the delicate hydraulic pressure regulation to be rendered by way of the modulator, which naturally is undesirable for the regular pressure control of the hydraulic system. Also, when there occasionally is entrapped air in the hydraulic line for relieving the braking pressure from the working system during the operation of the braking system because of breakage of the hydraulic line or because of a loose connection of the line, and when the thus entrapped air is redirected to the modulator, such condition would result in improper hydraulic pressure regulation of the modulator.
The present invention relates to the provision of a solution to such inconveniences and difficulties in the maintenance of proper hydraulic braking pressure regulation of the hydraulic pressure modulator or pressure regulating mechanism in a hydraulic braking system as experienced in a conventional hydraulic braking system for use in a vehicle.